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ST. PETERSBURG, Fla. -- Jeff Niemann appears to be finally pitching up to his potential.

Niemann took a perfect game into the fifth inning and wound up with a two-hitter, and Ben Zobrist hit a grand slam to help lead the Tampa Bay Rays to a 9-0 victory over the Kansas City Royals on Wednesday night.

"That was really fun to watch," Rays manager Joe Maddon said.

Niemann (5-4) retired his first 14 batters before Mark Teahen lined a two-out single to center in the fifth. The right-hander struck out a career-high nine and walked one in his first complete game.

The Royals other hit against the fourth overall selection in the 2004 amateur draft was a two-out infield single by Alberto Callaspo in the ninth. Niemann has been slowed by shoulder problems during his professional career.

"I've always felt that I can do that," Niemann said. "To come out here and do it, it was awesome. You get that confidence boost that you really can do it."

Niemann's outing was the eighth shutout with two or fewer hits by a Rays' pitcher, and the first since Matt Garza had a two-hitter last August 15 at Texas.

"He throws it hard and it breaks a lot," Teahen said of Niemann's breaking ball. "He was getting it over for strikes. He established that early and made it tough for us all day."

Zobrist became the first Rays' player with four career grand slams when he gave Tampa Bay an 8-0 lead in the fourth. He has two grand slams this year, with the other coming on April 17 against the Chicago White Sox.

"It makes it easy to hit when you're going out there and he's [Niemann] shutting the door time after time," Zobrist said. "He was on his game the whole time."

Zobrist's four grand slams came in a span of 195 at-bats, dating back to August 29, 2008.

Kansas City closer Joakim Soria got two outs in the eighth in his first outing since being sidelined May 7 with a right rotator cuff strain.

B.J. Upton hit a two-run double and later scored on a wild pitch by Brian Bannister (4-3) as Tampa Bay took a 4-0 lead in the second.

Bannister gave up eight runs, nine hits and three walks in 3 2/3 innings for the Royals, who have lost six in a row and 11 of 13.

"It's just a lack of production that leads to a lack of confidence," Royals manager Trey Hillman said of his teams' recent struggles. "We need some good at-bats back-to-back, and we need a pitcher to go out there and throw a heck of a game."

Bannister has lost two straight starts, allowing 15 runs over 8 2/3 innings.

"This one was all my fault," Bannister said.

Niemann is 3-1 in his last five starts. During that stretch he has given up eight runs in 31 innings.

Carlos Pena put the Rays ahead 1-0 on an RBI double during the first. Dioner Navarro had a solo homer in the fifth.

Tampa Bay has won four of five following a season-high five-game losing skid.

Game notes

Rays 3B Evan Longoria (left hamstring) didn't play. He could return to the lineup within a few days. ... Royals OF Coca Crisp (bereavement list) is expected to rejoin the team Thursday. ... Rays LF Carl Crawford stole two bases. He leads the majors with 33 stolen bases. ... RHP Luke Hochevar could be recalled from Triple-A Omaha to start Saturday's game at Toronto.